The use of microorganisms for synthesizing industrially important organic products is well known. Biosynthetic approaches for producing organic products can be extremely efficient when compared to large-scale chemical synthesis. Advantages a biosynthetic approach may have over a chemical synthetic approach for manufacturing an organic product include more rapid and more efficient product yield, isomeric purity, and reduced cost (see Thomas et al., 2002, Trends Biotechnol. 20: 238–42).
Lactic acid has wide industrial applicability, including uses in chemical processing and synthesis, cosmetics, pharmaceuticals, plastics, and food production. Lactic acid is a relatively simple organic molecule, and can be produced either by chemical synthesis or by fermentation in microorganisms (biosynthesis). As genetic manipulation of microorganisms has become more advanced, fermentation processes for lactic acid production have become commercially preferred over chemical synthesis. One reason for this preference is that using genetically modified microorganisms enables production of optically pure (i.e., either the L(+) or D(−) isomer) product. Such methods obviate the need for separating racemic product mixtures, thereby reducing cost.
Nevertheless, the use of microorganisms for producing organic products has certain limitations. For example, bacteria can produce large quantities of organic products under fermentation conditions, but the accumulation of organic products within the bacteria itself and in the growth medium can inhibit proliferation of the bacteria, or cause cell death. Even when more robust organisms are engineered and used for production, such as the acidophilic yeast Saccharomyces cerevisiae, organic products can lead to cell growth suppression, reducing overall yield of organic product. Thus, there remains a need in the art for robust microorganisms that are amenable to genetic manipulation, for use in bioreactors and with other biosynthetic methods for producing industrially important organic products.